Nafion–graphene nanocomposite film as enhanced sensing platform for ultrasensitive determination of cadmium

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Abstract

In this work, an ultrasensitive platform for the detection of cadmium (Cd2+) combining the nafion–graphene nanocomposite film with differential pulse anodic stripping voltammetry (DPASV) analysis was presented. It is found that this sensing platform exhibits enhanced response to the determination of the Cd2+ and has been used to determine the Cd2+ in real sample with good recovery.

Introduction

The wide use of cadmium in the electroplating, metallurgy, nickel–cadmium batteries, etc. poses severe harm for the environment and human health [1]. Exposure to lower amounts of Cd2+ can cause renal dysfunction, bone degeneration, lung insufficiency, liver damage and hypertension in humans with both acute and chronic toxicity [2], [3]. Accordingly, exploring facile techniques, enabling professionals to monitor cadmium temporally in the environment is of considerable significance. Prominent methods of analyzing Cd2+ are mainly based on the use of atomic absorption [4], [5] or inductively coupled plasma (ICP) atomic emission spectroscopy and ICP-mass spectrometry [6]. However, these spectrometric methods are expensive, and not suitable for the in situ measurement. As an alternative to these spectroscopy techniques, electroanalytical technique is one of the best methods for detecting metals due to its low cost, ease of use and reliability. Among all the electroanalytical techniques, anodic stripping voltammetry (ASV) with a mercury film has been recognized as a powerful tool for the trace measurement of Cd2+ [7]. Recently, to improve the sensitivity for the analysis of metal ions, the chemically modified electrode, heated electrodes, microwaved electrodes, and insonated electrodes have been exploited for the stripping analysis [8], [9], [10], [11], [12], [13]. Furthermore, the development of nanotechnology offers the great potential to increase the sensitivity of metal analysis. For example, incorporation of carbon nanotubes [14], [15] and ordered mesoporous carbon [16] has greatly improved the metal ions analysis capability due to the unique advantages: enhancement of the mass transport, high effective surface area and controllable electrode microenvironment [17].

Graphene, a monolayer of sp2 hybridized carbon atoms packed into a dense honeycomb crystal structure, has generated a great deal of interest to explore its fascinating applications from composite materials to quantum dots [18], [19], [20], [21], [22] since experimentally produced in 2004 [23]. Recently, graphene-based material has been developed as an advanced nanoelectrocatalyst for constructing electrochemical biosensors. For instance, Worden’s group [24], [25] has reported the use of the exfoliated graphite nanoplatelets to fabricate a high-performance glucose biosensor as a viable and inexpensive alternative to carbon nanotubes. These results indicate that graphene shows a grand potential as enhanced materials to fabricate the electrochemical sensing interface. However, no effort has been made to determine Cd2+ based on the graphene nanosheets.

Herein, a sensing platform for ultrasensitive determination of Cd2+ was presented based on the Nafion–graphene nanocomposite (Nafion–G) film modified electrode. The graphene was dispersed into the Nafion solution to form a homogeneous suspension, and then the Nafion–G film was obtained via a simple organic solvent evaporating. The interfusion of graphene into the pure Nafion film exhibited excellent stripping performance for trace analysis of Cd2+ combining the advantages of the graphene nanosheets (higher electrical conductivity, enlarged active surface area) together with the unique features of the mercury film.

Section snippets

Synthesis of graphene solution

Graphene oxide was synthesized according to the reported method with a slight modification [26], [27], [28]. In a typical procedure for chemical conversion of graphene oxide to graphene, the resulting graphene oxide dispersion (100 mL) was mixed with 70 μl of hydrazine solution (50 wt% in water) and 0.7 mL of ammonia solution (28 wt% in water). After being vigorously shaken or stirred for a few minutes, the solution was stirred for 1 h at the temperature of 95 °C.

Preparation of modified electrode

A 100 μL of 0.5 mg/ml graphene solution

Results and discussion

The structure and morphology of the resulting graphene were characterized using AFM. Fig. 1A indicated that the graphene sheets were almost single-layer. And the average thickness of single-layer graphene sheets was <1 nm. This unique nanostructure may be attractive as potential material for the determination of the metal ions. To prove the performance of graphene in the application of Cd2+ determination, the different voltammetric behaviors of the Nafion–G and Nafion modified electrode were

Conclusions

In summary, a new and highly enhanced sensing platform based on the Nafion–graphene nanocomposite film was established for the determination of Cd2+ by ASV. The nanocomposite film combining the advantages of graphene and the cationic exchange capacity of Nafion enhanced the sensitivity of Cd2+ assay. The practical application of the Nafion–G electrode was assessed. Furthermore, this simple sensing platform can not only be extended to the detection of other different heavy metal ions, on the

Acknowledgments

This work is supported by the National Natural Science Foundation of China with the Grants No. 20675076 and 973 Project 2009CB930100 as well as the support of 2006BAE03B08 from MOST.

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